Type 1 regulatory T cells are associated with persistent split erythroid/lymphoid chimerism after allogeneic hematopoietic stem cell transplantation for thalassemia

Abstract

BackgroundThalassemia major can be cured with allogeneic hematopoietic stem cell transplantation. Persistent mixed chimerism develops in around 10% of transplanted thalassemic patients, but the biological mechanisms underlying this phenomenon are poorly understood. Design and MethodsThe presence of interleukin-10-producing T cells in the peripheral blood of eight patients with persistent mixed chimerism and five with full donor chimerism was investigated. A detailed characterization was then performed, by T-cell cloning, of the effector and regulatory T-cell repertoire of one patient with persistent mixed chimerism, who developed stable split erythroid/lymphoid chimerism after a hematopoietic stem cell transplant from an HLA-matched unrelated donor. ResultsHigher levels of interleukin-10 were produced by peripheral blood mononuclear cells from patients with persistent mixed chimerism than by the same cells from patients with complete donor chimerism or normal donors. T-cell clones of both host and donor origin could be isolated from the peripheral blood of one, selected patient with persistent mixed chimerism. Together with effector T-cell clones reactive against host or donor alloantigens, regulatory T-cell clones with a cytokine secretion profile typical of type 1 regulatory cells were identified at high frequencies. Type 1 regulatory cell clones, of both donor and host origin, were able to inhibit the function of effector T cells of either donor or host origin in vitro. ConclusionsOverall these results suggest that interleukin-10 and type 1 regulatory cells are associated with persistent mixed chimerism and may play an important role in sustaining long-term tolerance in vivo. These data provide new insights into the mechanisms of peripheral tolerance in chimeric patients and support the use of cellular therapy with regulatory T cells following hematopoietic stem cell transplantation.Key words: thalassemia, hematopoietic stem cell transplantation, persistent mixed chimerism, tolerance, type 1 regulatory T (Tr1) cells.Citation: Serafini G, Andreani M, Testi M, Battarra MR, Bontadini A, Biral E, Fleischhauer K, Marktel S, Lucarelli G, Roncarolo MG, and

Quantitatively different red cell/nucleated cell chimerism in patients with long-term, persistent hematopoietic mixed chimerism after bone marrow transplantation for thalassemia major or sickle cell disease

“…21 Similar results were obtained by Felfly and Trudel in thalassemic mutant mice which were transplanted in order to determine the minimal percentage of normal bone marrow cells necessary to correct the thalassemic phenotype in a competitive re-population transplantation assay. 27 They found a 2-to 2.5-fold amplification of normal RBC compared to white blood cells in the peripheral blood of mice with 19-24% bone marrow chimerism, indicating an in vivo selective advantage for the normal RBC.…”

“…The potential role of T regulatory cells in establishing persistent mixed chimerism has been recently pointed out. [21][22][23][24] However, independently of the biological mechanisms involved, data from several studies have shown that patients with persistent mixed chimerism have clinical control of the disease, despite the presence of an extremely low proportion of donor nucleated cells. [10][11][12][13]25 The majority of studies concerning the assessment of persistent mixed chimerism have, however, almost exclusively focused attention on the percentage of donor engraftment in the nucleated cells rather than in the mature erythrocytes, cells functionally crucial for patients affected by hemoglobinopathies.…”

“…20 We very recently demonstrated the presence of a large majority of donor-derived RBC in a transplanted thalassemic patient with persistent mixed chimerism of nucleated cells by analyzing the differences between the donor and recipient surface erythrocyte markers using cytofluorimetry. 21 The aim of the present study was to determine the proportion of RBC and erythroid precursors of donor-recipient origin in long-term transplanted patients with persistent mixed chimerism, characterized by the presence of a low proportion of donor-derived nucleated cells in the peripheral blood and bone marrow.…”

Split chimerism between nucleated and red blood cells after bone marrow transplantation for haemoglobinopathies

“…[6][7][8] Therefore graft rejection probabilities were higher in patients with MC detected within the first months after the transplant and proportional to the amount 1 regulatory cells are associated with PMC and may play an important role in sustaining long-term tolerance in vivo. 11 Up to now, it is not clear if the mechanisms inducing an immunological tolerance in patients with PMC might also influence a different maturation of the donor erythroid precursors after HSCT for hemoglobinopathies. However, the presence of a split chimerism between mature erythrocytes and their progenitors has been recently described in persistent mixed chimera patients 13,14 with a predominant erythroid engraftment in the peripheral blood, while the proportion of erythroid precursors (BFU-E-burst forming unit erythroid) colonies and nucleated cells of donor origin in the bone marrow were equivalent (Fig.…”

What is the minimum level of donor chimerism necessary to sustain transfusion independence in thalassaemia?

“…A possible explanation could be the presence of high proportions of IL-10-producing type 1 regulatory cells (Tr1) in such patients, possibly as a result of MC providing chronic allogenic stimulus. 7 Endogenous IL-10 inhibits alloreactivity against both host and donor cells and may be responsible for the induction and maintenance of long-term tolerance. Such patients are reported to have a lower incidence of GVHD.…”